The present invention relates generally to azimuth determination apparatus for determining the forward direction of a moving body on the basis of earth magnetism, and more particularly to such an azimuth determination apparatus including means for cancellation of an output error of an azimuth sensor on the basis of information obtained by a circular movement of the moving body.
An important problem in azimuth detection apparatus for determining the forward direction of a moving body on the basis of earth magnetism relates to the correction of an output error, or offset, of azimuth sensor resulting from magnetism attached to the moving body or azimuth sensor. One approach to resolution of the problem, such as is disclosed in Japanese Patent Provisional Publication No. 58-24811, is to form a circular vector locus in accordance with two orthogonal component signals generated from the azimuth sensor during a circular movement of the moving body and then to detect the center of the vector locus using the maximum and minimum values of the respective two orthogonal component signals thereby correcting the signals from the azimuth sensor on the basis of the detected vector locus center.
In this azimuth determination apparatus as disclosed in the above-mentioned prior art, the decision of termination of the circular movement of the moving body is made by comparison between the azimuth vectors obtained by the outputs of the azimuth sensor before and after the circular movement of the moving body, that is, under the condition that the azimuth vectors before and after the circular movement become substantially equal to each other. However, according to this decision method, when the rotating direction of the moving body is changed during the circular movement, the azimuth vector before the circular movement may become substantially equal to an azimuth vector obtained in the course of the circular movement, or at the time of the change of the rotating direction. This causes an erroneous decision of termination of the circular movement and makes impossible detection of accurate maximum and minimum values, resulting in difficulty of accurate correction of the outputs of the azimuth sensor.